Fuel cells are being developed as a power source for electric vehicles and other applications. Fuel cells are known to include a variety of components including a proton exchange membrane, an anode, a cathode and gas distribution elements.
Fuel cells typically include a proton exchange or polymer electrolyte membrane (PEM) sandwiched between a cathode catalyst layer and an anode layer to form a membrane electrode assembly (MEA). Gas diffusion media (GDM) engage each of the cathode catalyst layer and the anode catalyst layer. The catalyst layers may be coated on the GDM, and such a structure is known as catalyst-coated diffusion media (CC-DM). Alternatively, the catalyst may be coated on the PEM, and such a structure is known as catalyst-coated membrane (CCM).
Heretofore, edge-protection using subgaskets have been applied in both CC-DM and CCM fuel cells. FIG. 1 illustrates a prior art CC-DM 30 which includes a first GDM 17 having an anode catalyst layer 14 coated thereon. A second GDM 18 having a cathode catalyst layer 16 coated thereon is also provided. A proton exchange membrane 12 is provided and a first subgasket 20 is positioned to cover a portion of the upper surface of the membrane 12 along the periphery thereof. A second subgasket 22 is positioned to cover a portion of the lower surface of the membrane 12 along the periphery thereof. The proton exchange membrane 12, first subgasket 20 and second subgasket are interposed between the anode CC-DM and cathode CC-DM.
FIG. 2 illustrates a prior art CCM 10 which include a proton exchange membrane 12 having a anode catalyst layer 14 coated on an upper surface of the membrane 12, and a cathode catalyst layer 16 coated on a lower surface of the membrane 12. A first subgasket 20 is positioned to cover a portion of the membrane 12 and a portion of the anode catalyst layer 14 along the peripheral edge of each. In a like manner, a second subgasket 22 is positioned to cover a portion of the membrane 12 and a portion of the cathode catalyst layer 16 along the peripheral edge of each. A tenting region, 24, may be formed and is defined by a small void between the GDM 17 or 18 and the anode 14 or cathode 16, respectively.
Durability testing, graphically illustrated in FIG. 3, has shown that prior-art CCMs, as depicted in FIG. 2 are considerably less durable than CC-DMs. CC-DMs routinely outlast CCMs in harsh conditions such as 95° C., 300 kPa (abs) and 75/50% Relative Humidity. As shown in FIG. 3, the beneficial effect of edge-protection in prior art CCMs is relatively minor (125 hours for edge-protected vs. 100 for un-protected). However, in the case of prior art CC-DMs there is a 3-fold increase in the lifetime of the MEAs from 300 to 900 hours for unprotected versus protected CC-DMs.
The present invention provides alternatives to the prior art.